Vaporizer for MOCVD and method of vaporizing raw material solutions for MOCVD

ABSTRACT

Disclosed is a vaporizer constituted of a dispersing section  8  and a vaporizing section  22.  The dispersing section  8  comprises a gas introduction port  4  for introducing a carrier gas  3  under pressure into a gas passage, means for feeding raw material solutions  5   a  and  5   b  to the gas passage, and a gas outlet  7  for delivering the carrier gas containing the raw material solutions to the vaporizing section  22.  The vaporizing section  22  comprises a vaporizing tube  20  having one end connected to a reaction tube of the MOCVD system and having the other end connected to the gas outlet  7  of the dispersing section  8,  and heating means for heating the vaporizing tube  20.  The vaporizing section  22  serves to heat and vaporize the raw material solution containing carrier gas  3  delivered from the dispersing section  8.  The dispersing section  8  includes a dispersing section body  1  having a cylindrical hollow portion, and a rod  10  having an outer diameter smaller than the inner diameter of the cylindrical hollow portion. The rod  10  has a spiral groove  60  formed in the external periphery closer to the vaporizing section  22,  the rod  10  being inserted into the cylindrical hollow portion.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a vaporizer for MOCVD and amethod of vaporizing raw material solutions for MOCVD.

[0003] 2. Description of the Related Arts

[0004] Problematic in the development of DRAMs is a reduction in storagecapacitance resulting from the miniaturization. Any measures are neededsince the capacitance has to be level with that in the precedentgeneration from the viewpoint of software errors or the like. As ameasure for this, increase in the capacitor area has been aimed at byintroducing a three-dimensional structure referred to as a stackstructure or a trench structure for cell structures exceeding 4M inaddition to the planer structure for 1M or less. A dielectric film hasalso been employed which consists of a thermal oxide film and a CVDnitride film laminated on the poly-Si from the thermal oxide film of thesubstrate Si (this laminated film is referred to commonly as an ONfilm). For 16M DRAM, in order to further increase the area contributingto the capacitance, there have been introduced stack types such as athick-film type making use of the side or a fin type utilizing the backof the plate as well.

[0005] Such three-dimensional structures have disadvantageously givenrise to an increase in the stages due to the complicated process and areduction in the yield due to the increased steps, rendering therealization in 256 Mbits or larger DRAMs difficult. For this reason,conceived as one way to further increase the integration degree withoutaltering the current DRAM structures was a switching of the capacitancedielectrics to ferroelectrics having a higher dielectric constant. Firstattention was paid as a dielectric thin film having a high dielectricconstant to a thin film of high-dielectric-constant single-metalparaelectric oxides such as Ta₂O₅, Y₂O₃ and HfO₂. The relativedielectric constants of Ta₂O₅, Y₂O₃ and HfO₂ are of the order of 28, 16,24, respectively, which are four to seven times that of SiO₂.

[0006] Nevertheless, application to 256M or larger DRAMs necessitates athree-dimensional capacitor structure. (Ba_(x)Sr_(1-x))TiO₃,Pb(Zr_(y)Ti_(1-y))O₃ and (Pb_(a)L_(1-a))(Zr_(b)Ti_(1-b))O₃ are promisingas materials having a higher relative dielectric constant than the aboveoxides and expected to be applicable to DRAMs. Similarly promising is aBi-based laminar ferroelectric material having a crystal structureextremely resembling the superconductor. From the viewpoint oflow-tension drive and good fatigue characteristics, remarkable attentionis being paid recently to SrBi₂TaO₉ referred to as Yl material inparticular.

[0007] The formation of SrBi₂TaO₉ ferroelectric thin film is typicallycarried out by means of practical and promising MOCVD (metal organicchemical vapor deposition).

[0008] Raw materials of the ferroelectric thin film are typically threedifferent organometallic complexes, Sr (DPM)₂, Bi(C₆H₅)₃ and Ta(OC₂H₅)₅,which are each dissolved in THF (tetrahydrofuran) solvent for use as asolution. DPM is an abbreviation of dipivaloylmethane.

[0009] Table 1 shows the respective material characteristics. TABLE 1BOILING POINT(° C.)/ PRESSURE (mmHg) MELTING POINT(° C.) Sr (DPM)₂242/14 78 Si (C₆H₅)₃ 270˜280/1 201 Ta (OC₂H₅)₅ 146/0.15 22 THE 67 −109

[0010] The system for use in MOCVD comprises a reacting section forsubjecting SrBi₂TaO₉ thin film raw material to a gas phase reaction anda surface reaction for film deposition, a feeding section for feedingSrBi₂TaO₉ thin film raw material and an oxidizing agent to the reactingsection, and a collecting section for collecting reaction productsobtained in the reacting section.

[0011] The feeding section is provided with a vaporizer for vaporizingthe thin film raw material.

[0012] Known techniques related to the vaporizer are illustrated in FIG.12. FIG. 12A shows a so-called metal filter method in which a rawmaterial solution heated to a predetermined temperature is drip fed to ametal filter used with the aim of increasing the area of contact betweenthe ambient gas and the SrBi₂TaO₉ ferroelectric thin film raw materialsolution.

[0013] This technique however has a deficiency that the metal filter maybecome clogged after several-times vaporizations, making the long-termuse difficult.

[0014]FIG. 12B depicts a technique in which 30 kgf/cm² of pressure isapplied to a raw material solution so as to allow the raw materialsolution to be emitted through 10 μm pores and expanded for evaporation,

[0015] This technique however entails a problem that the pores maybecome clogged as a result of several-times operations, rendering itdifficult to endure the long-term use.

[0016] In the event that the raw material solution is a mixture solutionof a plurality of organometallic complexes, e.g., Sr(DPM)₂/THF,Bi(C₆H₅)₃/THF and Ta(OC₂H₅)₅/THF and that this mixture solution isvaporized by heating, the solvent (THF in this case) having a highestvapor pressure will be vaporized earlier, with the result that theorganometallic complexes may be deposited and adhered onto the heatedsurfaces, blocking a stable feed of raw materials to the reactingsection.

[0017] Furthermore, it is demanded in order to obtain a film having agood uniformity by MOCVD that there should be presented a vaporized gaswithin which the raw material solutions have uniformly been dispersed.However, the above prior art has not necessarily met such a demand.

SUMMARY OF THE INVENTION

[0018] It is therefore an object of the present invention to provide avaporizer for MOCVD capable of long-term use without causing anyclogging or other inconveniences and ensuring a stable feed of rawmaterials to the reacting section.

[0019] Another object of the present invention is to provide a vaporizerfor MOCVD and a method of vaporizing raw material solutions for MOCVD,capable of obtaining a vaporized gas containing uniformly dispersed rawmaterial solutions.

[0020] According to a first aspect of the present invention there isprovided a vaporizer for MOCVD having a dispersing section and avaporizing section, wherein the dispersing section comprises a gaspassage formed in the interior, a gas introduction port for introducinga carrier gas under pressure into the gas passage, means for feeding araw material solution to the gas passage, a gas outlet for deliveringthe carrier gas containing the raw material solution to the vaporizinysection, and means for cooling the gas passage, and where in thevaporizing section comprises a vaporizing tube having one end connectedto a reaction tube of an MOCVD system and having the other end connectedto the gas outlet of the dispersing section, and heating means forheating the vaporizing tube, the vaporizing section serving to heat andvaporize the raw material solution containing carrier gas delivered fromthe dispersing section.

[0021] According to a second aspect of the present invention there isprovided a vaporizer for MOCVD having a dispersing section and avaporizing section, wherein the dispersing section comprises a gaspassage formed in the interior, a gas introduction port for introducinga carrier gas under pressure into the gas passage, means for feeding araw material solution to the gas passage, and a gas outlet fordelivering the carrier gas containing the raw material. solution to thevaporizing section, and wherein the vaporizing section comprises avaporizing tube having one end connected to a reaction tube of an MOCVDsystem and having the other end connected to the gas outlet of thedispersing section, and heating means for heating the vaporizing tube,the vaporizing section serving to heat and vaporize the raw materialsolution containing carrier gas delivered from the dispersing section,and wherein the dispersing section includes a dispersing section bodyhaving a cylindrical hollow portion, and a rod having an outer diametersmaller than the inner diameter of the cylindrical hollow portion, therod having at least one spiral groove formed in the external peripherythereof, the rod being inserted into the cylindrical hollow portion.

[0022] According to a third aspect of the present invention there isprovided a method of vaporizing a raw material solction for MOCVD,comprising the steps of drip-feeding the raw material solution to a gaspassage, jetting a carrier gas toward the drip-fed raw material solutionat the flow velocity of 50 to 300 m/s to thereby shear and atomize theraw material solution to obtain a raw material gas, and delivering theraw material gas to a vaporizing section for vaporization.

[0023] The above and other objects, aspects, features and advantages ofthe present invention will become more apparent from the followingdetailed description in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a sectional view of the major part of a vaporizer forMOCVD in accordance-with embodiment 1;

[0025]FIGS. 2A and 2B are a longitudinal sectional view andcross-sectional view, respectively, of the vaporizer for MOCVD inaccordance with the embodiment 1;

[0026]FIG. 3 illustrates an MOCVD system;

[0027]FIG. 4 is a front elevational view of a reserve tank;

[0028]FIG. 5 is a sectional view of the major part of a vaporizer forMOCVD in accordance with embodiment 2;

[0029]FIG. 6 is a sectional view of the major part of a vaporizer forMOCVD in accordance with embodiment 3;

[0030]FIGS. 7A and 7A are cross-sectional view showing variants, inaccordance with embodiment 4, of the gas passages of the vaporizer forMOCVD;

[0031]FIG. 8 is a sectional view of a vaporizer for MOCVD in accordancewith embodiment 5;

[0032]FIGS. 9A to 9C are a side elevational view, a sectional view takenalong a line X-X of FIG. 9A, and a sectional view taken along a line Y-Yof FIG. 9A, respectively, of a rod for use in the vaporizer for MOCVD inaccordance with the embodiment 5;

[0033]FIG. 10 is a side elevational view of a variant of the rod shownin FIG. 9A;

[0034]FIG. 11 is a graphic representation of the results of experimentseffected in embodiment 6; and

[0035]FIGS. 12A and 12B are schematic sectional side elevations of theconventional vaporizer for MOCVD.

DESCRIPTION OF THE INVENTION

[0036] Embodiment 1

[0037]FIG. 1 illustrates a vaporizer for MOCVD in accordance withembodiment 1.

[0038] The vaporizer of this embociiment is cons'cituted of a dispersingsection 8 and a vaporizing section 22. The dispersing section 8comprises a gas passage 2 formed in the interior of a dispersing sectionbody 1 constituting the dispersing section 8, a gas introduction port 4for introducing a carrier gas 3 under pressure into the gas passage 2,means (a raw material feed opening) 6 for feeding a raw materialsolution 5 to the carrier gas 3 passing through the gas passage 2, a gasoutlet 7 for delivering the carrier gas 3 containing the ciispersed rawmaterial solution 5 to the vaporizing section 22, and means (coolingwater) 18 for cooling the carrier gas 3 flowing through the gas passage2. The vaporizing section 22 comprises a vaporizing tube 20 having oneend connected to a reaction tube of the MOCVD system and having theother end connected to the gas outlet 7 of the dispersing section 8, andheating means (a heater) 21 for heating the vaporizing tube 20. Thevaporizing section 22 serves to heat anti vaporize the dispersed rawmaterial solution containing carrier gas 3 delivered from the dispersingsection 8.

[0039] This embodiment will hereinafter be descried in greater detail.

[0040] In this embodiment, a 4.50 mm dia. bore (cylindrical hollowportion) is formed in the interior of the dispersing section body 1. Arod 10 is centered in the bore, the rod 10 having an outer diameter(4.48 mm) smaller than the inner diameter of the bore. Thc gas passage 2is formed by a space defined between the dispersing section body 1 andthe rod 10. The rod 10 is fixed in position by screws 9 a, 9 b, 9 c and9 d. The gas passage 2 has a width of 0.01 mm.

[0041] The width of the gas passage 2 is preferably 0.005 to 0.10 mm.The width less than 0.05 mm may render the machining difficult. Thewidth exceeding 0.10 mm may necessitate use of a hign-pressure carriergas in order to increase the velocity of the carrier gas.

[0042] The gas introduction port 4 is provided at one end of the gaspassage 2. A source of carrier gas (e.g., N₂, Ar) not shown is connectedto the gas introduction port 4.

[0043] On its side at substantially the middle, the dispersing sectionbody 1 is provided with the raw material feed opening 6 communicatingwith the gas passage 2 so that the raw material solution 5 can drip downin the gas passage 2 in such a manner as to be dispersed on the carriergas passing through the gas passage 2.

[0044] At the other end of the gas passage 2 is provided the gas outlet7 which communicates with the vaporizing tube 20 of the vaporizingsection 22.

[0045] The dispersing section body 1 is formed with a space 11 throughwhich the cooling water 18 flows so that the flow of the cooling water18 through the space can cool the carrier gas flowing through theinterior of the gas passage 2. Alternatively, this space may besubstituted by a Peltier element or the like for cooling. Since theinterior of the gas passage 2 of the dispersing section 8 is affected byheat from the heater 21, the solvent of the raw material solution andthe organometallic complex will not vaporize at the same time in the gaspassage 2 but instead only the solvent may convert to vapor earlier. Thepossible vaporization of only the solvent is thus prevented by coolingthe dispersed solution containing carrier gas flowing through the gaspassage 2. It is important in particular to cool the downstream side ofthe raw material feed opening 6, so that cooling has to be made of atleast the downstream side of the raw material feed opening 6. Thecooling temperature is set to a temperature equal to or below theboiling point of the solvent. In the case of THF (tetrahydrofuran) Forexample, the cooling temperature is 67° C. or below. Particularattention is to be paid to the temperature at the gas outlet 7.

[0046] Furthermore, cooling of the dispersing section can prevent theinterior of the gas passage (gas outlet especially) from being blockedoff by carbides during the long-term use.

[0047] The dispersing section body 1 is connected to the vaporizing tube20 downstream of the dispersing section body 1. A fitting 24 provides aconnection between the dispersing section body 1 and the vaporizing tube20 to define a connecting section 23.

[0048] The vaporizing section 2.2 consists of the vaporizing tube 20 andthe heating means (heater) 21. The heater 21 serves to heat and vaporizethe carrier gas containing the dispersed raw material solution flowingthrough the interior of the vaporizing tube 20, The heater 21 can be forexample the Peltier element attached to the external periphery of thevaporizing tube 20.

[0049] The vaporizing tube 20 is made preferably of stainless steel suchas SUS316L for example. The dimensions of the vaporizing tube 20 can bedetermined in an appropriate manner as of {fraction (3/4)} inches inouter diameter and of 100 mm in length,

[0050] The vaporizing tube 20 is connected at its downstream end to thereaction tube of the MOCVD system and is provided in this embodimentwith an oxygen feed opening 25 serving as oxygen feed means so as toallow oxygen heated to a predetermined temperature to be mixed into thecarrier gas.

[0051] Description will first be made of start of feed of the rawmaterial solution to the vaporizer,

[0052] As shown in FIG. 3, reserve tanks 32 a, 32 b, 32 c and 32 d areconnected to the raw material feed opening 6 by way of mass flowcontrollers 30 a, 30 b, 30 c and 30 d, respectively, and of valves 31 a,31 b, 31 c and 31 d, respectively.

[0053] A carrier gas cylinder 33 is connected to the reserve tanks 32 a,32 b, 32 c and 32 d.

[0054] Details of the reserve tanks are depicted in FIG. 4.

[0055] The reserve tanks are each filled with the raw material solution.3 kgf/cm² of carrier gas is fed into each reserve tank (made of SUS withinternal volume of 300 cc). The interior of the reserve tank ispressurized by the carrier gas so that the raw material solution ispushed up through the tube in contact with the solution and is fed underpressure to the mass flow controller for liquid (made of STEC with fullscale flow rate of 0.2 cc/min) by means of which the flow rate iscontrolled, The raw material solution is further delivered through a rawmaterial feed inlet 29 of the vaporizer to the raw material feed opening6.

[0056] It is then carried to a reacting section by the carrier gas whoseflow rate has been controlled to a certain value by means of a mass flowcontroller (made of STEC with full scale flow rate of 2 L/min). At thesame time, oxygen (oxidizing agent) is also delivered to the reactingsection, with the flow rate of oxygen being controlled to a certainvalue by means of a mass flow controller (made of STEC with full scaleflow rate of 2 L/min).

[0057] The raw material solution contains an organometallic complexwhich is dissolved in THF as the solvent and is liquid or solid at thenormal temperature. Hence, if it is left to stand, the THF solvent willevaporate, allowing the organometallic complex to deposit and finallybecome solidified. It is therefore envisaged that the interior of thepiping in contact with the raw material solution may possibly becomeclogged thereby. A cleansing line is thus provided under considerationthat the interiors of the piping and vaporizer have only to be cleansedby THF after the completion of the film forming work in order tosuppress any possible clogging of the piping. Cleansing is performedover the segment extending from the outlet of the mass flow controllerfor liquid to the vaporizer and includes washing off by THF after thecompletion of the work.

[0058] The valves 31 b, 31 c and 31 d were opened so that the carriergas was fed under pressure into the reserve tanks 32 b, 32 c and 32 d,respectively. The raw material solution is then delivered under pressureto the mass flow controller (made of STEC with full scale flow rate of0.2 cc/min) by means of which the flow rate is controlled, the resultantraw material solution being fed to the raw material feed opening 6 ofthe vaporizer.

[0059] On the other hand, the carrier gas was introduced through the gasintroduction port of the vaporizer. It is to be noted that too a highpressure of the carrier gas may possibly cause the rod 10 to project.Therefore, the maximum pressure on the feed opening side is preferably 3kgf/cm² or less. The maximum permissible flow rate at that time is ofthe order of 1200 cc/min, and the passage flow rate in the gas passage 2can reach one hundred and several tens of meters per second.

[0060] When the raw material solution drips down from the raw materialfeed opening 6 onto the carrier gas flowing through the gas passage 2 ofthe vaparizer, the raw material solution is sheared by the high-velocityflow of the carrier gas and becomes ultrafine. As a result of this, theraw material solution is dispersed in the form of ultrafine particlesinto the carrier gas. The carrier gas (raw material gas) containing theraw material solution dispersed in the form of ultrafine particles isdischarged into the vaporizing section 22 while keeping its highvelocity,

[0061] Three different raw material solutions having flow ratescontrolled to certain values flow via the respective raw material feedinlets 29 and through the raw material feed opening 6 into the gaspassage 2 to move through the gas passage together with the carrier gasin the form of a high-velocity air flow, after which they are dischargedinto the vaporizing section 22. In the dispersing section 8 as well, theraw material solution is heated by heat from the vaporizing section 22and vaporization of THF is accelerated, so that the segment from the rawmaterial feed inlets 29 to the raw material feed opening 6 and thesegment of the gas passage 2 are cooled down by tap water.

[0062] After the discharge from the dispersing section 8, the rawmaterial solutions dispersed in the form of fine particles within thecarrier gas are subjected to accelerated vaporization during thedelivery through the interior cf the vaporizing tube 20 heated to apredetermined temperature by the heater 21 and mix with oxygen heated toa predetermined temperature from the oxygen feed opening 25 providedimmediately short of the reaction tube for the MOCK!. The raw materialsolutions thereby result in mixed gases, which flow into the reactiontube.

[0063] A vacuum pump not shown was connected to an exhaust port 42 andwas operated for pressure reduction for twenty minutes to removeimpurities such as moistures lying within the reaction tube 44, afterwhich a valve 40 downstream of the exhaust port 42 was closed.

[0064] Cooling water was supplied to the vaporizer at approximately 400cc/min. On the other hand, 3 kgf/cm² of carrier gas was fed at 495cc/min so that the interior of the reaction tube 44 was fully filledwith the carrier gas, after which the valve 40 was opened. Thetemperature at the gas outlet 7 was lower than 67° C.

[0065] The interior of the vaporizing tube 20 was heated to 200° C., thesegment from the reaction tube 44 to a gas pack 46 and the gas pack 46were heated to 100° C., and the interior of the reaction tube 44 washeated to 300° C. to 600° C.

[0066] The interior of the reserve tank was pressurized by the carriergas, and the mass flow controller was used to flow a predeterminedliquid therethrough.

[0067] Sr(DPM)₂, Bi(C₆H₅)₃, Ta(OC₂H₅)₅ and THF were flowed at the flowrate of 0.04 cc/min, 0.08 cc/min, 0.08 cc/min and 0.2 cc/min,respectively.

[0068] Twenty minutes later, the valve immediately upstream of the gaspack 46 was opened so that reaction products were collected In the gaspack 46. The reaction products were analyzed by gas chromatograph to seewhether detected products coincided with products in the reactionformula examined on the basis of the react ion theory. The result wasthat in this embodiment the detected products were well coincident withthe products in the reaction formula examined on the basis of thereaction theory.

[0069] The amount of adhesion of carbides on the external surface of thedispersing section body 1 toward the gas outlet 7 was measured. Theresult was that the amount of adhesion of carbides was extremely small.

COMPARATIVE EXAMPLE 1

[0070] This example used an apparatus similar to the apparatus shown inFIG. 1 but excluding the cooling means therefrom, in order to makesimilar experiments.

[0071] In this example, sufficient coincidence was not obtained betweendetected products and products in the reaction formula examined on thebasis of the reaction theory.

[0072] The result of measurement of the amount of adhesion of carbideson the external surface of the dispersing section body 1 toward the gasoutlet 7 was about five times the amount of adhesion of carbides in thecase of the embodiment 1.

[0073] Embodiment 2

[0074]FIG. 5 illustrates a vaporizer for MOCVD in accordance withembodiment 2.

[0075] In the embodiment 1 the connecting section 23 was also subjectedto heating by the heater 21, whereas in this embodiment the heater wasprovided only around the external periphery of the vaporizing section22. Instead, cooling means 50 were provided around the externalperiphery of the connecting section 23 to cool the connecting section23.

[0076] The others were the same as the embodiment 1.

[0077] In this embodiment, better coincidence was obtained than in thecase of the embodiment 1 between detected products and products in thereaction formula examined on the basis of the reaction theory.

[0078] The result of measurement of the amount of adhesion of carbideson the external surface of the dispersing section body 1 toward the gasoutlet 7 was about one third the amount of adhesion of carbides in thecase of the embodiment 1.

[0079] Embodiment 3

[0080]FIG. 6 illustrates a vaporizer for MOCVD in accordance withembodiment 3.

[0081] in this embodiment, the interior of the connecting section 23 hasa tapered portion 51 with larger inner diameters from the dispersingsection 8 toward the vaporizing section 22, Such a tapered portion 51serves to eliminate any dead zones and contributes to the prevention ofpossible residence of the raw material.

[0082] The others were the same as the embodiment 1.

[0083] In this embodiment, better coincidence was obtained than in thecase of the embodiment 2 between detected products and products in thereaction formula examined on the basis of the reaction theory.

[0084] Measurement of the amount of adhesion of carbides on the externalsurface of the dispersing section body 1 toward the gas outlet 7resulted in substantially no adhesion of carbides.

[0085] Embodiment 4

[0086]FIGS. 7A and 7B illustrate a modification of the gas passage.

[0087] In FIG. 7A, the rod 10 has the surface provided with grooves 70and has the outer diameter substantially equal to the inner diameter ofthe bore formed in the interior of the dispersing section body 1. Thus,by merely fitting the rod 10 into the bore, it is possible to positionthe rod 10 in the bore without permitting any eccentricity. There is noneed to use screws. The grooves 70 serve as gas passages.

[0088] It will be understood that a plurality of grooves 70 may beformed in such a manner as to extend in parallel with the longitudinalaxis of the rod 10 although a spiral groove may be formed around thesurface of the rod 10. In the case of the spiral groove, a more uniformraw material gas will be obtained.

[0089] In the embodiment of FIG. 7B, the rod 10 is provided withprotrusions. The maximum diameter of the protrusions is substantiallyequal to the inner diameter of the bore formed in the interior of thedispersing section body 1. Gas passages are spaces defined by theprotrusions and the internal surface of the bore.

[0090] Although FIGS. 7A and 7B iliustrate the rod 10 having themachined surface by way of embodiment, it is natural that the rod maybeof a circular section, with the bore being formed with recesses todefine the gas passages.

[0091] Embodiment 5

[0092] Embodiment 5 is then described with reference tc FIG. 8.

[0093] The vaporizer of this embodiment is constituted of a dispersingsection 8 and a vaporizing section 22. The dispersing section 8comprises a gas passage formed in the interior, a gas introduction port4 for introducing a carrier gas 3 under pressure into the gas passage,means for feeding raw material solutions 5 a and 5 b to the gas passage,and a gas outlet 7 for delivering the carrier gas 3 containing the rawmaterial solutions 5 a and 5 b to the vaporizing section 22. Thevaporizing section 22 comprises a vaporizing tube 20 having one endconnected to a reaction tube of the MOCVD system and having the otherend connected to the gas cutlet 7 of the dispersing section 8, andheating means for heating the vaporizing tube 20. The vaporizing section22 serves to heat and vaporize the raw material solution containingcarrier gas 3 delivered from the dispersing section 8. The dispersingsection 8 includes a dispersing section body 1 having a cylindricalhollow portion, and a rod 10 having an outer diameter smaller than theinner diameter of the cylindrical hollow portion. The rod 10 has one ormore spiral grooves 60 formed in the external periphery closer to thevaporizing section 22, the rod 10 being inserted into the cylindricalhollow portion.

[0094] When the raw material solutions 5 a and 5 b are Ted to the gaspassage through which the carrier gas 3 flows at a high velocity, theraw material solutions are sheared and atomized. That is, the rawmaterial solutions in the form of liquid are sheared and reduced toparticles by the high-velocity flow of the carrier gas. The particulateraw material solutions are dispersed as fine particles into the carriergas. In this respect, the embodiment 5 is similar to embodiment 1.

[0095] In order to optimize the shearing and atomization, the followingconditions are preferred.

[0096] The raw material solutions 5 a and 5 b are fed at preferably 0.01to 1 cc/min, more preferably 0.05 to 0.5 cc/min, and most preferably 0.1to 0.3 cc/m n. In the case of simultaneous feed of a plurality of rawmaterial solutions (inclusive of the solvent), the rate of feed isrepresented by the total amount thereof.

[0097] The carrier gas is fed at the rate of preferably 50 to 300 m/escand more preferably 100 to 200 m/sec.

[0098] In this embodiment, the rod 10 has on its external periphery aspiral groove 60, with the presence of a gap space defined between thedispersing section body 1 and the rod 10, whereby the carrier gascontaining the atomized raw materiai solutions can flow straight as astraightforward flow through the gap space and can form a spiral flowalong the spiral groove 60.

[0099] The inventors have thus found out that the atomized raw materialsolutions can uniformly disperse into the carrier gas in the state wherethe straightforward flow and the spiral flow are coexistent. It is notnecessarily apparent why the uniform dispersion can be obtained when thestraightforward flow and the spiral flow coexist. The reason may howeverbe envisaged as follows. The presence of the spiral flow allows acentrifugal force to act on the flow, with the result that a secondaryflow will occur. The secondary flow accelerates the mixture of the rawmaterial solutions and the carrier gas. More specifically, thecentrifugal effect of the spiral flow causes a secondary, derivativeflow to be generated in the direction perpendicular to the flow,whereupon the atomized raw material solutions will disperse moreuniformly into the carrier gas.

[0100] This embodiment will hereinafter be described in greater detail.

[0101] In this embodiment, four different raw material solutions 5 a, 5b, 5 c and 5 d (5 a to 5 c are organometallic raw materials, and 5 d isa solvent raw material such as THF) are fed to the gas passage by way ofembodiment.

[0102] In order to mix the carrier gas (referred to as “raw materialgas”) containing raw material solutions which have each been atomizedand reduced to ultrafine particles, the rod 10 of this embodiment isprovided with a spiral groove free portion downstream of the portioncorresponding to the raw material feed opening 6. This spiral groovefree portion forms a premixing section 65. In the premixing section 65the three different organometallic raw material gases are mixed to someextent, and in the downstream region of spiral structure they arereduced to a perfect raw material mixture gas. To attain a uniform rawmaterial mixture gas, the length of this mixing section 65 is preferablywithin a range from 5 to 20 mm, and more preferably 8 to 15 mm. Outsideof this range, the vaporizing section 22 may accept a raw materialmixture gas having a higher concentration of only one organometallic rawmaterial gas of the three.

[0103] In this embodiment, the upstream end portion 66 of the rod 10 isprovided with a parallel portion 67 and a tapered portion 58. In amanner corresponding to the parallel portion 67 and the tapered portion58, the cylindrical hollow portion of the dispersing section body 1 isalso provided with a parallel portion having the inner diameter equal tothe cuter diameter of the parallel portion of the rod 30 and with atapered portion having the same taper as that of the tapered portion ofthe rod 10. Thus, by inserting the rod 10 from left in the diagram, therod 10 can be retained in the hollow portion of the dispersing sectionbody 1.

[0104] Unlike the case of the embodiment 1, this embodiment employs therod 10 provided with the taper for retention so that the rod 10 isprevented frcm being displaced upon the use of a high-pressure carriergas exceeding 3 kgf/cm². In other words, employment of the retentiontechnique shown in FIG. 8 ensures that the carrier gas can flow under apressure equal to or higher than 3 kg/cm². As a result of this, itbecomes possible to feed a higher velocity of carrier gas. Thus, itbecomes also possible to feed a high-velocity carrier gas of 50 to 300mm/s. The same will apply to the other embodiments set forth hereinaboveby employing this retention technique.

[0105] It is to be noted that at the portion corresponding to the rawmaterial feed opening 6 the rod 10 is formed with grooves 67 a, 67 b, 67c and 67 d acting as carrier gas passages as seen in FIG. 9B. The depthof the grooves 67 a, 67 b, 67 c and 67 d is preferably 0.005 to 0.1 mm.The depth less than 0.005 mm will make the groove forming workdifficult. More preferably, the range of depth is 0.01 to 0.05 mm. Thisrange can obviate any possible clogging or other inconveniences. Ahigh-velocity flow is also easy to obtain.

[0106] The features of the embodiment 1 shown in FIG. 1 or otherfeatures may be employed for the retention of the rod 10 and formationof the gas passage(s).

[0107] A single spiral groove 60 may be formed as shown in FIG. 9A, butinstead a plurality of spiral grooves 60 may be formed as shown in FIG.10. In the case of formation of the plurality of spiral grooves, theymay cross. In the event of crossing, a more uniformly dispersed rawmaterial gas is obtained.

[0108] The dimensions and contours of the spiral groove(s) 60 are notlimited to any particular ones, although FIG. 9C depicts one examplethereof.

[0109] It is to be noted in this embodiment that the gas passage iscooled by the cooling water 18 as shown in FIG. 8.

[0110] In this embodiment, an expanding section 69 is separatelyprovided upstream of the entrance to the dispersing section 22. Thisexpanding section 69 corresponds to the portion provided for preventingthe residence cf the raw material gas in the embodiment 3. It is naturalthat the expanding section 69 may not necessarily be separately providedbut that it may be integrally formed as shown in FIG. 6.

[0111] The angle θ of expansion of the expanding section 69 ispreferably within a range from 5 to 10 degrees. In case the angle θ lieswithin this range, it is possible to feed the raw material gas to thedispersing section without breaking the spiral flow. Additionally, incase the angle θ lies within this range, the fluid resistance due to theexpansion is minimized, with the minimum presence of dead zones sc thatthe occurrence of eddy flows due to the presence of the dead zones canbe minimized. More preferably, the angle θ is within a range from 6 to 7degrees. The embodiment shown in FIG. 6 has also the same preferredrange of θ.

[0112] Embodiment 6

[0113] In order to examine the uniformity of the raw material gas, theapparatus shown in FIG. 8 was used to feed the raw material solutionsand carrier gas under the following conditions. Amount of drip-feed ofraw material solutions: 2 2 Sr (DPM)₂ 0.04 cc/mm Bi (C₆H₅)₃ 0.08 cc/mmTa (OC₂H₅)₅ 0.08 cc/mm THE  0.2 cc/mm

[0114] Carrier gas:

[0115] nitrogen gas 10 to 350 m/s

[0116] The vaporizer used was the apparatus shown in FIG. 8. Used as therod was a rod similar to that shown in FIGS. 9A to 9C but having nospiral grooves.

[0117] The raw material solutions were fed through the raw material feedopening 6, with the carrier gas being fed at various speeds. Through theraw material feed opening, Sr(DPM)₂, Bi(C₆H₅)₃, Ta(OC₂H₅)₅ and THE werefed to grooves 67 a, 67 b, 67 c and 67 d, respectively.

[0118] The vaporizing section was not subjected to heating. The rawmaterial gas was sampled at the gas outlet 7. Measurement was made ofparticle diameters of raw material solutions in the sampled raw materialgas.

[0119] The results are shown as relative values in FIG. 11 (where 1represents a value obtained when the apparatus in accordance with theconventional example was used). As is apparent from FIG. 11, thediameters of dispersed particles become small when the flow velocityexceeds 50 m/s, and the dispersed particle diameters become even smallerwhen 100 m/s is exceeded. At the velocity exceeding 200 m/s, however,the diameters cf the dispersed particles become saturated. A morepreferred range is therefore 100 to 200 m/s.

[0120] Embodiment 7

[0121] In this embodiment, the spirally grooved rod was used. The otherswere the same as the embodiment 6.

[0122] In the embodiment 6, the raw material solutions fed to thegrooves had high concentrations in the extensions of the grooves. Morespecifically, the concentrations of Sr(DPM)₂, Bi(C₆H₅)₃ and Ta(OC₂H₅)₅were high at their respective extensions of the grooves 67 a, 67 b and67 d, respectively.

[0123] In this embodiment, however, the raw material mixture gasobtained at the end of the spiral groove contained uniformorganometallic raw materials at every portions.

[0124] According to the present invention there can be provided avaporizer for MOCVD capable of long-term use without causing anyclogging or other inconveniences and ensuring a stable feed of rawmaterials to the reacting section.

[0125] According to the present invention there can be obtained avaporized gas containing uniformly dispersed organometallic materials.

What is claimed is:
 1. A vaporizer for MOCVD having a dispersing sectionand a vaporizing secticn, whereir. said dispersing section comprises: agas passage formed in the interior; a gas introduction port forintroducing a carrier gas under pressure into said gas passage; meansfor feeding a raw material solution to said gas passage; a gas outletfor delivering said carrier gas containing said raw material solution tosaid vaporizing section; and means for cooling said gas passage; andwherein said vaporizing section comprises: a vapcrizing tube having oneend connected to a reaction tube of an MOCVD system and having the otherend connected to said gas cutlet of said dispersing secticn; and heatingmeans for heating said vaporizing tube; said vaporizing section servingto heat and vaporize said raw material solution containing carrier gasdelivered from said dispersing section.
 2. A vaporizer for MOCVDaccording to claim 1, further comprising cooling means for cooling aportion connecting said dispersing section and said vaporizing section.3. A vaporizer for MOCVD according to claim 1 or 2, wherein said portionconnecting said dispersing section and said vaporizing section istapered with reduced inner diameters from said vaporizing section towardsaid dispersing section.
 4. A vaporizer for MOCVD according to one ofthe claims 1 through 3, wherein said dispersing section comprises adispersing section body having a cylindrical hollow portion, and a rodhaving an outer diameter smaller than the inner diameter of saidcylindrical hollow portion, said rod being inserted into saidcylindrical hollow portion.
 5. A vapozizer for MOCVD according to one ofclaims 1 through 3, wherein said dispersing section comprises adispersing section body having a cylindrical hollow portion, and a rodhaving an outer diameter substantially equal to the inner diameter ofsaid cylindrical hollow portion, said rod having at least one grooveformed in the external periphery thereof, said rod being inserted intosaid cylindrical hollow portion.
 6. A vaporizer for MOCVD according toclaim 5, wherein said groove is a rectilinear groove.
 7. A vaporizer forMOCVD according to claim 5, wherein said groove is a spiral groove.
 8. Avaporizer for MOCVD having a dispersing section and a vaporizingsection, wherein said dispersing section comprises: a gas passage formedin the interior; a gas introduction port for introducing a carrier gasunder pressure into said gas passage: means for feeding a raw materialsolution to said gas passage; and a gas outlet for delivering saidcarrier gas containing said raw material solution to said vaporizingsection; and wherein said vaporizing section comprises: a vaporizingtube having one end connected to a reaction tube of an MOCVD system andhaving the other end connected to said gas outlet of said dispersingsection; and heating means for heating said vaporizing tube; saidvaporizing section serving to heat and vaporize said raw materialsolution containing carrier gas delivered from said dispersing section;and wherein said dispersing section includes a dispersing section bodyhaving a cylindrical hollow portion, and a rod having an outer diametersmaller than the inner diameter of said cylindrical hollow portion; saidrod having at least one spiral groove formed in the external peripherythereof, said rod being inserted into said cylindrical hollow portion.9. A vaporizer for MOCVD acccrding to claim 8, further comprisingcooling means for cooling said gas passage.
 10. A vaporizer for MOCVDaccording to claim 8 or 9, further comprising cooling means for coolinga portion connecting said dispersing section and said vaporizingsection.
 11. A vaporizer for MOCVD according to one of claims 8 through10, wherein said portion connecting said dispersing section and saidvaporizing section is tapered with reduced inner diameters from saidvaporizing section toward said dispersing section,
 12. A vaporizer forMQCVD according to one of claims 8 through 11, wherein said rod has anelectropolished surface.
 13. A vaporizer for MOCVD according to one ofclaims 8 through 12, further comprising cooling means for cooling saidgas passage.
 14. A vaporizer for MOCVD according to one of claims 8through 13, further comprising cooling means for cooling a portionconnecting said dispersing section and said vaporizing section.
 15. Avaporizer for MOCVD according to one of claims 8 through 14, whereinsaid portion connecting said dispersing section and said vaporizingsection is tapered with reduced inner diameters from said vaporizingsection toward said dispersing section.
 16. A method of vaporizing a rawmaterial solution for MOCVD, comprising the steps of: drip-feeding saidraw material solution to a gas passage; jetting a carrier gas towardsaid drip-fed raw material solution at the flow velocity of 50 to 300m/s to thereby shear and atomize said raw material solution to obtain araw material gas; and delivering said raw material gas to a vaporizingsection for vaporization.
 17. A method of vaporizing a raw materialsolution for MOCVD according to claim 16, wherein said raw materialsolution is drip fed at 0.01 to 1 cc/min.
 18. A method of vaporizing araw material solution for MOCVD according to claim 16 or 17, whereindownstream of the portion drip-fed with said raw material solution, saidcarrier gas or saici raw material gas flows in a coexistent manner as aspiral flow and a straightforward flow flowing over said spiral flow.19. A method of vaporizing a raw material solution for MOCVD accordingto one of claims 15 through 18, wherein said raw material gas is cooledin the region from the portion drip-fed with said raw material solutionup to said vaporizing section.